The science of Gaia and future challenges Sep. 1, 2017 JASMINE series ★ JASMINE ー Japan Astrometry Satellite Mission for INfrared Exploration － ～ Today I focus on the Small-JASMINE mission ～ Naoteru Gouda Director of JASMINE Project Office, NAOJ 1 1
◎ Japanese group is promoting space astrometry missions, JASMINE projects series, in international collaboration with Gaia DPAC team. JASMINE missions are complementary to Gaia mission. 2030s(target) 2023 (target)- 2020(target)- 2
１． Outline of Small-JASMINE We have been aiming at the realization of the Small-JASMINE mission as a mission of the small science satellite program executed by JAXA. Astrometric Measurement in Hw-band (1.1 µ m~1.7 µ m) Infrared astrometry missions have advantage in surveying the Galactic nuclear bulge, hidden by interstellar dust in optical bands! Two survey modes １． survey for the key project in spring and autumn Nuclear bulge around the Galactic center 2. survey for open use in summer and winter some directions toward interesting target objects (e.g CygX-1, planetary systems Advantage of Small-JASMINE: every 100 minutes! of brown dwarfs, star-forming regions High frequent measurements of the same target besides the area near the center) 3 3 Phenomena with short periods
★ The details of the survey mode for the key project （ toward the Galactic nuclear bulge) Survey region 1: the circle with the radius of 0.7 degree ( ～ 100pc) around the Galactic center ・ the number of observable stars <=high precisions bulge stars: ~4900(Hw<12.5mag) of parallax(20µas) ( disk stars in front of the bulge: ～ 3500(Hw<12.5) common with stars measured by Gaia ) This survey region makes it possible to determine whether or not relatively small supermassive black holes merge to form the supermassive black hole at the Galactic center. Please refer to the scientific objective A-1. Survey region 2: Survey region: Galactic longitude -2.0 ～ 0.5 degree Galactic latitude 0.2 ～ 0.5 degree This survey region makes ・ the number of observable stars it possible to determine whether bulge stars : ~5000 (Hw<12.5mag) <=high precisions an inner bar exists. Please refer ( disk stars in front of the bulge: of parallax(20µas) 4 to the scientific objective A-2 ～ 1600 (Hw<12.5))
The number density of observable stars(Hw<12.5) estimated by the use of the combination of 2MASS and the Guide Star Catalogue(GSC) The number of stars /( 1dgree × 1 degree) Galactic longitude Galactic latitude 5
Astrometric Precisions in the key survey mode: parallax and position: < ~20 µ µ as for Hw<12.5mag proper motion: < ~20 µ µ as/yr for Hw<12.5mag ( photometry(Hw-band): ＜ 0.01 mag ) Small-JASMINE will provide data of parallaxes, proper motions and time sequences of stellar positions on the celestial sphere in the survey region of the key project. 6
★ Survey mode for open use in summer and winter seasons We will accept mission proposals for open call to scientific communities in the world and the time allocation committee will select targets and their priority. Examples of candidates of scientific targets: X-ray binaries (e.g. CygX-1), γ -ray binaries, planetary systems of brown dwarfs, star-forming regions besides the area near the center, etc. *the precisions of astrometric parameters of target objects depend on each target while the precisions are restricted by the designed system of the satellite. 7
★ Complement of the Gaia mission in Small-JASMINE ＊ Gaia can measure only about ～ 80 bulge stars with high precisions(<20µas precision of the parallax) which are located in the same region as the whole survey region of Small-JASMINE around the Galactic center due to the effect of absorption by the interstellar dust. SJ (Small-JASMINE) => ～ 8900 bulge stars Small-JASMINE ＊ Gaia can measure the same target every 40 days. So Gaia cannot resolve the astrophysical phenomena with much shorter periods than around 40 days. SJ=> every 100 minutes although the survey regions are restricted. *IAU Commission A1 (astrometry) recommends Small- JASMINE for its unique infrared space astrometry 8 mission! 8
２． Scientific Objectives SJ will provide scientific outputs over the widely spread fields of astronomy and astrophysics. ★ Examples of scientific objective of Small-JASMINE A. Astrophysics around the Galactic center 9
Scientific Objectives A-1 ． Formation of the supermassive black hole at the Galactic center Merging of black holes and/or Accretion of gas? Small-JASMINE=>Proof of merging of intermediate BHs １． If intermediate mass BHs( above 100,000 solar mass: the total mass is 4 million solar mass) exit and they have fallen into the Galactic center(<100pc) by the dynamical friction, è the effect of the dynamical friction (and the release of the gravitational energy of BH binaries) “heat up” the stars around the center area(<100pc). 2 ． The heated up density profile and the distribution of the velocity dispersion: the universal function independent of mass distribution and the number of BHs (core radius ～ 100pc:independent of the initial density profile of the bulge) ＊ Self-similar evolution to the universal functions (Merritt et al. 2004, Tanikawa & Umemura 2014) For example, SJ’s data will determine whether the stellar distribution within 100pc from the Galactic center corresponds to the universal function with more than 99.7% confidence 10 level.
Scientific Objectives A-2. Gravitational potential at the Galactic nuclear bulge Small-JASMINE’s data will constrain models of the gravitational potential in the Galactic nuclear bulge region (within ~300pc away from the Galactic center) with the phase space density of stars *Gas accretion to the Galactic center Gas fueling is very important for the growth of SMBH, activities of galactic nuclei, nuclear star bursts and the formation of super star clusters in the Galactic central region. *need to clarify transport mechanism of gas to the Galactic center ◎ candidate of key processes for transportation of gas : rotating bar=>Losing angular momentum and energy of gas Existence of an inner bar? <=suggestion of existence by the spatial distribution of stars Gas transportation from CMZ=>within 10pc SJ will suggest the existence of the inner bar by the difference of the pattern speed. For example, SJ will determine whether the pattern speed of the inner bar is much different from that of the outer bar with more than 99.7% confidence level. *the pattern speed of the outer bar: 35 ～ 50km/s/kpc 11 *the pattern speed of the inner bar if it exit:stability condition=>more than170km/s/kpc
Scientific Objectives A-3. Motion of star clusters around the Galactic center è the birth places of star clusters A-4. Discovery of unknown stellar clusters in the nuclear bulge by detection of parallel movement of the stellar proper motions è clarification of star formation rates A-5. Discovery of Hyper Velocity Stars(HVS) in the nuclear bulge è clarification of the origins of HVS and S-stars * Stellar binary+ SMBH or single star + IMBH-SgrA* binary A-6. Analysis of symbiotic X-ray binaries è the origin of X-ray emission spread along the galactic plane(!?). 12
Scientific Objectives A-7. Discovery of unknown BHs (i) Residual from a helical motion è discovery of BH-star binaries è analysis of orbit element è clarification of BH mass (ii) Astrometric microlensing *ref: the first detection of the astrometric microlensing effect due to celestial objects outside the solar system (HST: Sahu, et al., 2017) è Determination of the mass of the white drawf Stein2015B! A-8. Discovery of exoplanets by the use of astrometric microlensing : A-9. Discovery of unknown objects e.g. Wormholes?! A-10. Stellar physics, Star formation ＊ 3-Ddistribution of inter -stellar dust ＊ annual parallax and proper motions of Mira-type variable stars in the bulge 13
Scientific Objectives B: Astrophysics besides the direction toward the Galactic nuclear bulge Open use time (in summer and winter seasons): less than 50% of the total observation time Good candidates: phenomena with short periods, bright objects in infrared bands B-1. Compact celestial objects Determination of the orbit elements of X-ray binaries and γ -ray binaries è Big revolution! è physics of accretion disk and jets, etc. *a good candidate of X-ray binary ： Cyg X-1:(l=71 ° , b=+3 ° ) period:5.6 days( unmeasurable by Gaia) companion star: mv~9mag , change of the position: 40~50µas measurable by Small-JASMINE è identification of compact objects * γ Cas: WD or NS=>1s degree of confidence, HESS J0632: NS or BH (2s) B-2. Extra-planets detection of planets by astrometric method *determination of mass with precisions of <20% for stars measured by radial velocities *primary star: low-mass star(late M-dwarf, brawn dwarf): H=10mag,V=16-18mag 14 B-3. Analysis of stellar hot spots
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